This invention relates to vehicular wheels upon which inflatable tires may be mounted. Such wheels are commonly employed in the transportation industry in automobiles, vans, trucks and the like.
In the past, wheels employed for transportation uses have been formed of wrought steel. While such steel wheels operate satisfactorily, with the ever-increasing need for fuel economy, both for economic and conservation purposes, several attempts have been made to replace these steel wheels with wheels formed of aluminum and its alloys. When employing aluminum vehicular wheels, significant weight reduction can be realized over similar wheels formed of steel.
Two choices can be made for employing aluminum wheels to replace steel wheels. The aluminum wheels may be either metal worked or cast. The term "metal worked" is meant to include such operations as extrusion, forging, stamping, coining, swaging, embossing and the like.
Cast aluminum wheels have an advantage in that the wheels may be formed with intricate stylized face surfaces such that when employing a cast aluminum wheel no added-on hubcap or other decorative feature is required for aesthetic purposes. This feature is desirable, since added-on hubcaps may be lost or stolen. However, due to the porosity, dynamic fatigue life, yield strength and elongation properties of cast aluminum, wheels formed from cast aluminum, while still significantly lighter than steel wheels, are not as light as could be hoped for by replacing steel with aluminum.
Metal worked aluminum wheels, on the other hand, may be formed significantly lighter than even cast aluminum wheels. This is due to the superior physical properties for structures formed of metal worked aluminum over those formed of cast aluminum. For example, an extruded or forged 6061-T6 aluminum alloy has a yield strength of approximately 38,000 PSI (185,500 kilograms per square meter) while a cast aluminum alloy No. 356 has a yield strength of approximately 16,000 to 18,000 PSI (78,100 to 87,900 kilograms per square meter). The elongation of the extruded or forged alloy is a minimum 14% while the cast alloy has an elongation of approximately 2-7%. Thus, a 14 inch by 5.5 inch (35.6 by 12.9 centimeter) extruded or forged aluminum wheel of 6061-T6 alloy weighs approximately 11.25 pounds (5.10 kilograms) while a cast aluminum wheel formed of 356 alloy and of equivalent strength weighs approximately 16 pounds (7.26 kilograms). Thus, the extruded or forged aluminum wheel is approximately 30% lighter than the equivalent cast aluminum wheel.
Metal worked aluminum wheels, however, have a disadvantage from the stylist point of view. Similar to forged steel wheels, metal worked aluminum wheels cannot be formed with the intricate stylized faces which can readily be formed in cast aluminum wheels. Thus, similar to forged steel wheels, metal worked aluminum wheels have been designed in the past to accept an added-on hubcap or other stylizing face which, as previously mentioned, is subject to being lost or stolen.
It is desirable, therefore, to form an integral aluminum wheel having the strength properties of a metal worked aluminum wheel and the stylizing advantages of a cast aluminum wheel, and while taking full advantage of the weight reduction properties of aluminum over steel.